Symptoms of low back and leg pain are at least partially responsible for thousands of lost workdays, and 20 to 100 billion dollars in health care costs each year in the United States alone. Numerous distinguished clinicians and researchers have stated that specific causes for symptoms can not be diagnosed in many of these patients. Despite the cost to society and the recognized limitations of current diagnostic techniques, few improved diagnostic techniques have been developed, and even fewer have been proven to be clinically useful. Approximately 20 percent of hospitalized back pain patients are diagnosed with spinal stenosis. This diagnosis is based on the hypothesis that insufficient space available for neural elements in the spine can cause low back and leg pain. This hypothesis is supported by years of clinical experience, yet it is commonly recognized that there are many exceptions. The diagnosis of spinal stenosis is typically based on qualitative assessments made from x-ray, CT and/or MRI data. Limited quantitative guidelines have been described but they are not in widespread use, in part because threshold levels of stenosis that are sensitive and specific for symptoms have never been proven. Technology to reproducibly measure spinal stenosis from common imaging modalities is readily available. Society will benefit from this technology after guidelines for obtaining and using quantitative measurements are validated. New diagnostic tests can be validated using measurements that represent positive and negative findings. Many patients with spinal stenosis have little or no pain in some positions and moderate to severe pain in other positions. These patients may cross a threshold level of stenosis by changing the position of their spine. This important and common clinical observation points to powerful model that can be used to validate quantitative measurements of spinal stenosis, since ach patient can serve as their own control. The specific aims of the proposed research are to identify specific measurements of spinal stenosis that are sensitive and specific for symptoms, and to identify the co-factors that effect the association between spinal stenosis and back or leg pain. Several different quantitative measurements will be made to account for the many possible types of stenosis. Measurements will be made non-invasively three-dimensional computer reconstructions of the spine in a painful position and compared to measurements made with the spine in a less painful position. Psychosocial variables will also be recorded to account for the role of these variables in the relationships between spinal stenosis and symptoms. This investigation will be conducted at a large university based spine center that has an established clinical outcomes program, established access to imaging data, and will use validated measurement techniques. The proposed investigations will provide clinically applicable measurements guidelines for the assessment of spinal stenosis.